TiO₂ Photocatalyzed Degradation of the Azo Dye Disperse Red 1 in Aqueous Micellar Environments^†

Abstract

The photoinduced degradation of the azo dye Disperse Red 1 was studied in a microheterogeneous system comprising titanium oxide (TiO2) and sodium dodecyl sulfate, exposed to UV light. Degussa P25, Anatase and TiO2 synthesized in acidic conditions were supported on raschig rings. The TiO2 photocatalyzed degradation is enhanced in the vicinity of the surfactant critical micelle value. Further increase on the surfactant concentration leads to a loss in photodegradation performance up to values equivalent to that observed without surfactant. Surfactant influence can be explained by two different phenomena taking place. The increasing concentration of surfactant leads to an increase in micellar concentration, inducing the incorporation of the dye to the hydrophobic moiety of the micelles, rendering the hydroxyl radical unable to interact with the dye. Similarly, the increased concentration of micelles at the photocatalyst/water interface might lead to a decrease in the number of active sites on the TiO2 surface able to either generate reactive species and/or interact with de dye molecules. Additives such as H2O2, NaCl, Na2SO4, and Na2CO3 are able to override the influence of the surfactant both positively and negatively, being the final outcome of the influence highly dependent on the crystalline form of the TiO2 photocatalyst.

Kinetic effects of cationic surfactants on the photocatalytic degradation of anionic dyes in aqueous TiO2 dispersions

“…11 Surfactants also play a key-role in this topic, generally favoring the photodegradation process of organic pollutant dyes in different pH conditions. [12][13][14][15] The degradation enhancement by TiO2 was mainly attributed to the increased adsorption of pollutant dyes, assisted by differently aggregated surfactants present on the solid surface of the semiconductor. In this context, still little explored, we have previously reported the employment of amphiphilic molecules combined with Degussa P25 TiO2 as a strategy to reduce the coupling electron-hole, as able to increase the adsorption of the donor (an organic compound) on TiO2 surface.…”

Photochemical Synthesis of Lactic Acid Esters at Ambient Temperature Employing Sulfonically Fuctionalized N/W‐Doped Nano‐semiconductor

“…This photochemical approach termed as artificial photocatalysis combines the efficiency of the catalyst, with the potential use of light photons and employing the chemistry of different electron holes such as semiconductor oxides (20)(21). Although this light-induced technique is well known for its application in the photochemical degradation of various inorganic and organic pollutants (22)(23)(24)(25)(26)(27) into mineralized products, its relevance as a technological and energy-efficient solution for organic synthesis reactions is still in the emerging phase. The prospective use of TiO 2 for the conversion of biomass into fuels and other synthetic chemicals inspired our enormous interest in replacing current technology for a wide range of ester synthesis.…”